What is Formwork?
Formwork is a temporary structure used to create the form of the desired structure before it is permanently constructed. It is used as a mold to hold the concrete and other materials in place until it sets.
Types of Formwork Material: Formwork material selection depends on several factors like cost, structure type, and requirements. Different materials are available for constructing the formwork, such as wood, steel, plastic, and aluminum. Each type has its own advantages and disadvantages.
Advantages and Disadvantages of Different Formwork Materials: Wood: Wood is the most commonly used formwork material due to its light weight and easy availability. However, it is prone to warping, cracking, and rotting over time.
Steel: Steel is strong and durable, making it ideal for high-stress applications. However, it is more expensive than other materials and requires a lot of effort to install.
Plastic: Plastic is lightweight and easy to install. It is also reusable, making it a cost-effective choice. However, it is not as strong as other materials and can be easily damaged.
Aluminum: Aluminum is lightweight, durable, and corrosion-resistant, making it a great choice for outdoor applications. However, it is more expensive than other materials and requires special tools for installation.
Different Formwork Materials
Different formwork materials and their advantages and disadvantages are discussed below.
- Timber
- Plywood
- Steel
- Aluminum
- Plastics
- Magnesium
- Fabric
1. Timber as Formwork Material
Timber is the most commonly used material for formwork, making it a traditional formwork option. This is due to its economical nature and easy handling. Timber logs, lumber and other timber materials are commonly used as bracing members. Some advantages of using timber as formwork material include: 1. Easy to Cut into Any Size: Timber is easy to cut into any required size. 2. Lightweight and Easy to Handle: Timber is light in weight, making it easy to handle. 3. Good Thermal Resistance: Timber has good thermal resistance, preventing damage to concrete in colder regions. 4. Easy to Understand Construction Method: The construction method of timber formwork is well understood, so skilled workers are not necessarily required. 5. Easy to Replace Damaged Parts: Damaged parts of timber forms are easy to replace. 6. Easy Dismantling: Timber formwork can be easily dismantled.
Disadvantages of Timber as Formwork Material:
Although there are some advantages to using timber as formwork material, it also has some disadvantages. These include: 1. Absorption of Water: Dry timber may absorb water from wet concrete and reduce the strength of the concrete structure. 2. High Moisture Content: Wet timber with high moisture content may compress wet concrete and cause cracks in the structure. Grout may also leak through joints when shrinking occurs. 3. Limited Usage: Timber forms have limited usage, so they cannot be used multiple times.
2. Plywood as Formwork Material
Plywood as Formwork Material: Plywood is a manufactured timber product that is increasingly used for formworks due to its smooth finish and cost-effectiveness. It consists of a number of veneer sheets or plies layered together. Exterior plywood is the special type used for formwork, since these boards are watertight due to strong adhesives used to bond the veneer sheets. Plywood boards with thicknesses ranging from 7mm to 32mm are available, and the most common size is 1220 x 2440 with an 18mm thickness. Special types of plywood are also available for curved structures.
Advantages of Plywood Formwork: Plywood formwork is strong, durable and light in weight, and can be easily cut into the required size. It provides a smooth finish on the surface which reduces finishing costs, and large size plywood sheets are available which makes the formwork construction quicker and easier. Plywood formwork can also be used for curved structures and offers more reuses when compared to timber.
Disadvantages of Plywood Formwork: Plywood formwork is more expensive than timber, and thin plywood sheets cannot sustain the weight of concrete and may bow out if not provided with the right thickness.
3. Steel as Formwork Material
Steel as Formwork Material: Steel can be an ideal formwork material due to its durability, strength and reusability. It is used in mass structures such as dams and bridges, providing an excellent finish to the concrete surfaces. However, it is very costly and requires lifting equipment for large structures.
Advantages of Steel Formwork: Steel forms are durable and stronger than other materials, providing a uniform and smooth surface finish to the structure. It is also easy to fix and dismantle, and can be reused multiple times.
Disadvantages of Steel Formwork: The major disadvantage of steel formwork is its cost; it is much higher than other materials. It is also heavy in weight and corrosion can occur if it is frequently exposed to water. Additionally, the size and shapes of forms available are limited.
4. Aluminum as Formwork Material
Advantages of Using Aluminum Formwork: Aluminum formwork is becoming increasingly popular due to its light weight and good strength. This type of formwork requires fewer supports and ties, making it easier to fix and dismantle. Additionally, aluminum formwork can be re-used multiple times and allows for the simultaneous casting of walls and slabs. Monolithic, crack free structures are also achievable when using aluminum formwork.
Disadvantages of Using Aluminum Formwork: The main disadvantage of using aluminum formwork is that when the load reaches its maximum limit, the lighter sections may deflect. Additionally, architectural modifications are not possible when using aluminum formwork.
5.Plastics as Formwork Material
Advantages of Plastics as Formwork Material: Plastic is a lightweight and durable formwork material that is typically used for small concrete structures or complex portions of the structure. It offers many advantages, including being easy to handle, resistant to water, and having the ability to be recycled and reused.
Disadvantages of Plastics as Formwork Material: Although plastic is a useful formwork material, it does have some drawbacks. It is relatively expensive and weak against heat, and it does not take much load when compared to other materials.
6.Magnesium as Formwork Material
Introduction to Magnesium Formwork: Magnesium is a metal element which can be used in formwork construction. Magnesium is not used directly but in conjunction with oxygen atoms which form magnesium oxide, also known as magnesia or MgO. MgO boards are available in various sizes and grades for use in formwork.
Advantages of Using Magnesium in Formwork: MgO boards have many advantages, such as being light in weight and easy to handle, fireproof, and waterproof. Additionally, they are considered bio-friendly, meaning they won’t cause harm to the environment. Furthermore, they are strong enough to resist heavy loads.
Disadvantages of Using Magnesium in Formwork: There are some disadvantages to using MgO boards for formwork. When MgO boards come into contact with wet concrete, the magnesium chloride present can dissolve and corrode the reinforcements. Additionally, skilled supervision is required for installation, and MgO boards are not suitable for humid conditions as they absorb moisture easily and are often referred to as “crying boards”.
7.Fabric as Formwork Material
Advantages of Fabric as Formwork Material: Fabric formwork is the modern technology in construction sector, which is becoming increasingly popular due to its lightweight and economical nature. It has many advantages, such as its ability to be molded into any required shapes, making it an ideal formwork material for architectural purposes. It is also waterproof and won’t affect the properties of the concrete, and is easy to remove after the concrete has hardened.
Disadvantages of Fabric as Formwork Material The main disadvantage of fabric as formwork material is that it requires skilled workers for its installation, in order to create the perfect, complex shapes. Furthermore, it is much lighter than other formwork materials, which means that it isn’t as strong and may be more prone to deformations.
